Multicomponent Copper Alloy and Its Use

ABSTRACT

The invention relates to a multicomponent copper alloy comprising [in % by weight]: Ni from 1.0 to 15.0%, Sn from 2.0 to 12.0%, Mn from 0.1 to 5.0%, Si from 0.1 to 3.0%, balance Cu and unavoidable impurities, if desired up to 0.5% of P, if desired individually or in combination up to 1.5% of Ti, Co, Cr, Al, Fe, Zn, Sb, if desired individually or in combination up to 0.5% of B, Zr, S, if desired up to 5% of Pb, and having Mn—Ni silicide phases which have a mass ratio of the elements [w(Mn)+w(Ni)]/w(Si) in the range from 1.8/1 to 7/1.

The invention relates to a multicomponent copper alloy and to its use.

Wrought alloys based on copper-nickel-tin have been known for a longtime. For example, U.S. Pat. No. 1,535,542 describes such an alloy inconjunction with the aim of improving the material properties withrespect to corrosion resistance, ductility and formability.

U.S. Pat. No. 1,816,509 discloses a copper-nickel-tin alloy and a methodfor the further treatment of such alloys. After casting the alloy, themethod involves a cold forming process and, in order to adjustparticular material properties, a heat treatment for homogenizing andage hardening the alloy. The heat treatment leads to continuous anddiscontinuous precipitates with the formation of a further γ phase.

Specification DE 41 21 994 C2 discloses a further method by which acopper-nickel-tin alloy as a wrought alloy for friction-bearing elementapplications undergoes conventional steps of casting and forming, the γphase being formed as continuous and discontinuous precipitates by aheat treatment after the last cold forming. The volume fraction of the γphase which is formed depends on the process management selected for theheat treatment.

Further to this, numerous studies have been carried out in the system ofcopper-nickel-tin alloys (U.S. Pat. No. 4,142,918, U.S. Pat. No.4,406,712 and WO 2005/108631 A1) in order constantly to refine thematerial properties. In practice, it has however been found that manyproperty combinations, for example wear resistance and thermalstability, cannot be optimized simultaneously by the known processtechnology. The improvement in one material property is then obtained atthe cost of another property, which is likewise important for certainapplication fields.

It is therefore an object of the invention to refine a multicomponentcopper alloy so that both a high, mechanical wear resistance and a highthermal stability are achieved.

The invention is characterized with respect to a multicomponent copperalloy by the features of claim 1 and with respect to a use by thefeatures of claim 13. The other dependent claims relate to advantageousconfigurations and refinements of the invention.

The invention provides a multicomponent copper alloy consisting of [in %by weight]:

Ni 1.0 to 15.0%, Sn 2.0 to 12.0%, Mn 0.1 to 5.0%, Si 0.1 to 3.0%,

remainder Cu and unavoidable impurities,optionally up to 0.5% P,optionally individually or in combination up to 1.5% Ti, Co, Cr, Al, Fe,Zn, Sb,optionally individually or in combination up to 0.5% B, Zr, S,optionally up to 5% Pb,with Mn—Ni silicide phases, which have a mass ratio of the elements[w(Mn)+w(Ni)]/w(Si) in the range of from 1.8/1 to 7/1.

The invention is based on the idea of providing a multicomponent copperalloy which simultaneously offers very good wear resistance and,particularly for use as a friction-bearing element in a thermallystressed environment, excellent thermal stability. With silicon ormanganese contents exceeding the specified maximum values of 3% byweight and 5% by weight, respectively, the alloy is susceptible toembrittlement which entails difficulties in the further treatment, inparticular owing to edge cracks in the strip material during rolling.Addition of the elements Ti, Co, Cr and Fe leads to the formation offurther silicide phases. Sb and Al may be added owing to the improvementin the low-friction properties or the corrosion resistance. The furtherelements B, Zr and S serve to deoxidize the melt or make a contributionto the grain refinement. The element phosphorus likewise serves fordeoxidation, although it can also form phosphide phases which make animportant contribution to increasing the hardness of the matrix. Theelement lead is relevant to the production of cast alloys, while inwrought alloys it is not present or present in very small amounts.

The Mn—Ni silicide phases according to the invention, which have a massratio of the elements [w(Mn)+w(Ni)]/w(Si) in the range of from 1.8/1 to7/1, serve in particular to increase the contact area ratio infriction-bearing element applications. Particularly with somewhatincreased manganese proportions, the alloy according to the inventionhaving Mn—Ni silicide phases forms an increasingly fine grain structurewhich in principle leads to an advantageous increase in the elongationat break A5.

The wrought Cu—Ni—Sn alloys according to the invention are spinoidallydemixing systems, which are particularly suitable as bearing materialsin motor construction as a solid material and in compositefriction-bearing elements. These materials have good friction and wearproperties as well as good corrosion resistance. The thermal stabilityis also excellent.

With Ni contents of from 1 to 15% by weight and Sn contents of from 2 to12% by weight, cold forming factors of up to 60% can be achieved forthese materials. In combination with soft annealing, it is possible toproduce thin strips suitable for material composites. These alloys mayalso be age hardened in the temperature range between 300 and 500° C.The material is thereby strengthened owing to the spinoidal demixingwhich takes place. Furthermore, continuous or discontinuous precipitatesmay be generated. This form of precipitation hardening is far superiorto binary copper-based alloys.

Compared with copper-based alloys and conventional Cu—Ni—Sn alloys, theadvantages achieved by the invention are in particular that the materialproperties can be adapted optimally to the respective task by means ofrolling, homogenization annealing and age hardening. For example, asofter or harder multicomponent copper alloy may be combined bymechanical and thermal treatment in composite friction-bearing elementswith harder materials, for example steel.

Advantageously, the mass fraction of the elements satisfies thefollowing relationship: [w(Ni)−w(Mn)−w(Sn)]>0. In other words, thenickel content is greater than the tin and manganese contents together,since nickel should be contained both for the silicide formation and forthe spinoidal demixing in the ideal case in the same proportions as tin.Not only are intermetallic phases thereby formed, which increase thecontact area ratio in friction-bearing applications and also reduce thewear in jack connectors. In parallel with this, a hardness increasethrough spinoidal demixing can be achieved with respect to the matrix bya heat treatment.

In an advantageous configuration, the mass fraction of the elements maysatisfy the following relationship: w(Mn)>w(Si). If the manganesecontent is more than the silicon content, sufficient manganese will beavailable for the silicide formation. Surprisingly, further grainrefining is observed in the matrix when the manganese content isincreased beyond the silicon content.

Advantageously, the value of the elongation at break A₅ at a temperatureof 400° C. is more than 10%. The alloy according to the inventiontherefore exhibits ductile behavior. This is primarily attributable tograin refining. In a temperature range of from room temperature to about400° C., the elongation at break lies at an almost constant level of18-20%. Comparable alloys without silicide components, conversely,exhibit a pronouncedly brittle behavior. For these alloys, under thesame conditions, an elongation at break value of from 8 to 15% isobtained, although this falls to a value of only 4% beyond about 300° C.This effect is analogous to the so-called strain ageing effect to beobserved in long-term stored or heat treated seals. A comparableembrittling effect is also known for bronzes.

In a preferred configuration, the crystallite size of the Mn—Ni silicidephases may be from 0.1 to 100 μm. In this case there are sometimes alsoelongated particles in the matrix. For friction-bearing applications,such particle sizes are particularly advantageous with respect to thefriction-bearing pair in question.

The alloy may advantageously contain from 0.01 to 0.06% P, finelydistributed Ni phosphide phases being formed in the matrix. These phaseshave a hardness increasing effect for the matrix. Even with a proportionof about 100 ppm, a significant increase in the hardness can beachieved. Advantageously, the average grain size of the finelydistributed Ni phosphide phases may be less than 100 nm.

In a particular configuration of the invention, the multicomponentcopper alloy may contain from 0.1 to 2.5% Mn and from 0.1 to 1.5% Si. Ithas been found that modified Cu—Ni—Sn variants with an Si content of upto 1.5% by weight and an Mn content of up to 2.5% by weight can bemanufactured with an improvement in the material properties. Furtherlaboratory tests have likewise already been carried out in this regard,and have confirmed the limiting values.

In this way, the approach of achieving a further improvement in the wearresistance of Cu—Ni—Sn alloys by the formation of hard intermetallicphases is pursued. These further hard material phases involvemanganese-nickel silicides. Cu—Ni—Sn alloys per se already exhibit verygood properties with respect to the low-friction properties, corrosionresistance and relaxation or resistance at room temperature. The hardphases which are formed also reduce the susceptibility to adhesion inthe mixed friction range and further increase the thermal stability andthe ductility at higher temperatures.

By combining the structural components contributing to the wearresistance in conjunction with the spinoidally demixing alloy of theCu—Ni—Sn system, surprisingly on the one hand it is possible to reducethe run-in behavior at the start of stress due to wear, and on the otherhand such a Cu—Ni—Sn—Mn—Si material turns out to be just as thermallystable as well as sufficiently ductile.

The multicomponent copper alloy may advantageously contain from 0.1 to1.6% Mn and from 0.1 to 0.7% Si. In particular, it has been establishedthat it is in fact possible to manufacture without problems in terms ofmanufacturing technology with an Si content of up to 0.7% by weight andan Mn content of up to 1.6% by weight. With high silicon and manganesecontents, corresponding adaptations should be carried out for thecasting parameters in the context of standard precautions.

The multicomponent copper alloy may advantageously undergo at least oneheat treatment at from 300 to 500° C. The material is therebystrengthened owing to the spinoidal demixing which takes place.

In a preferred configuration of the invention, the multicomponent copperalloy may undergo at least one heat treatment at from 600 to 800° C. Theheat treatment in this range leads to homogenization, which makes thematerial more ductile.

In a particularly preferred configuration of the invention, themulticomponent copper alloy may undergo a combination of at least onesolution anneal at from 600 to 800° C. and at least one age hardening atfrom 300 to 500° C. The material is thereby strengthened owing to thespinoidal demixing which takes place. The heat treatment in this rangeleads to homogenization, which makes the material softer. Owing to ahomogenizing anneal and the hardening of the material during agehardening or rolling, the material properties of the multicomponentcopper alloy can be adapted optimally to the respective task.

In another preferred configuration, the multicomponent copper alloy maybe employed for friction-bearing elements or jack connectors.

Exemplary embodiments of the invention will be explained in more detailwith the aid of the following example and the scanning electronmicroscope image shown in FIG. 1.

EXAMPLE

In series of tests, blocks with various Mn—Si ratios were cast andsubsequently cold-processed further. The alloy variants studied arecollated in Table 1. The cast blocks were homogenized in the temperaturerange of between 700 and 800° C. and then milled.

Strips with thicknesses of between 2.5 and 2.85 mm were produced by aplurality of cold forming operations and intermediate anneals. Thestrips were cold-rolled and annealed in the temperature range of between700 and 800° C., in order to achieve sufficient cold forming properties.

TABLE 1 Cu—Ni— Cu Ni Sn Mn Si Sn + Mn + Si [wt. %] [wt. %] [wt. %] [wt.%] [wt. %] Variant 1 remainder 5.6-6.0 5.2-5.6 1.7-2.0 0.2-0.3 Variant 2remainder 5.6-6.0 5.2-5.6 1.3-1.6 0.2-0.3 Variant 3 remainder 5.6-6.05.2-5.6 1.3-1.6 0.5-0.7 Variant 4 remainder 5.6-6.0 5.2-5.6 0.8-1.00.1-0.3 Variant 5 remainder 5.6-6.0 5.2-5.6 0.8-1.0 0.3-0.5 Variant 6remainder 5.6-6.0 5.2-5.6 0.4-0.6 0.4-0.6 Variant 7 remainder 5.6-6.05.2-5.6 0.9-1.1 0.9-1.1 Variant 8 remainder 5.6-6.0 5.2-5.6 1.8-2.10.5-0.5 Variant 9 remainder 5.6-6.0 5.2-5.6 1.8-2.1 0.9-1.1

According to expectation, it was confirmed that the cold formability ofthe Cu—Ni—Sn alloy modified with silicides is somewhat less than in thecase of a Cu—Ni—Sn alloy without further silicide phases.

Such strips may be combined in a further method step to form a firmmaterial composite by roll-cladding methods. Cu—Ni—Sn alloys modifiedwith suicides have a much lower coefficient of friction compared withthe silicide-free variant. The alloy according to the invention istherefore suitable in particular as a primary material for use as afriction-bearing element (bushings, thrust rings, etc.) in therespective automotive field for motors, transmissions and hydraulics.

FIG. 1 shows a scanning electron microscope image of the surface of amulticomponent copper alloy. The relatively finely distributedmanganese-nickel silicides 2, which are embedded in the alloy matrix 1,may be seen clearly. These silicides are already formed in the melt asan initial precipitate in a temperature range around 1100° C. With asuitable choice of the melt composition, the available silicon andmanganese precipitates with a nickel component present in excess to formthe silicide. The nickel component thereby consumed in the silicide maycorrespondingly be taken into account for the subsequent formation ofthe matrix by a higher nickel component in the melt.

The composition of the silicides need not necessarily correspond to apredetermined stoichiometry. Depending on the process management, and inparticular determined by the cooling rate, ternary intermetallic phasesprecipitate in the form of silicides of the (Mn,Ni)_(x)Si type, whichlie in the range between the limiting-case binary phases Mn₅Si₃ andNi₂Si.

The mechanical properties of strips of the multicomponent copper alloycontaining silicides in the rolling-hardened state had a tensilestrength Rm of 560 MPa and a yield point of 480 MPa with an elongationat break A5 of 25%. The hardness HB was about 176.

After age hardening the strips, a tensile strength Rm of 715 MPa and ayield point Rp_(0.2) of 630 MPa with an elongation at break A₅ of 17%were found. The hardness HB was about 235.

FIG. 2 shows a diagram with measurement values of the elongation atbreak A₅ for multicomponent copper alloys according to the inventionwith silicide phases having been formed (curves D and E) andconventional multicomponent copper alloys of the generic type (curves A,B, C) without silicide phases. The different values of elongation atbreak at room temperature are attributable to a different age hardeningtemperature in the range of between 300 and 500° C. With temperaturesbeyond about 250° C., the value for the elongation at break A₅ fallsbelow 10% for all samples in which no silicide phases are formed. Onlyin alloys according to the invention does this value remainsignificantly more than 10% throughout the temperature range from roomtemperature to 400° C. In the present case, it even remains above 15%.The alloy according to the invention is therefore much more ductile thanthe previously known comparable alloys without manganese and silicon.

1. Multicomponent copper alloy consisting of [in % by weight]: Ni 1.0 to15.0%, Sn 2.0 to 12.0%, Mn 0.1 to 5.0%, Si 0.1 to 3.0%, remainder Cu andunavoidable impurities, optionally up to 0.5% P, optionally individuallyor in combination up to 1.5% Ti, Co, Cr, Al, Fe, Zn, Sb, optionallyindividually or in combination up to 0.5% B, Zr, S, optionally up to 5%Pb, with Mn—Ni silicide phases, which have a mass ratio of the elements[w(Mn)+w(Ni)]/w(Si) in the range of from 1.8/1 to 7/1.
 2. Multicomponentcopper alloy according to claim 1, characterized in that the massfraction of the elements satisfies the following relationship:[w(Ni)−w(Mn)−w(Sn)]>0.
 3. Multicomponent copper alloy according to claim1, characterized in that the mass fraction of the elements satisfies thefollowing relationship: w(Mn)>w(Si).
 4. Multicomponent copper alloyaccording to claim 1, characterized in that the value of the elongationat break A₅ at a temperature of 400° C. is more than 10%. 5.Multicomponent copper alloy according to claim 1, characterized in thatthe crystallite size of the Mn—Ni silicide phases is from 0.1 to 100 μm.6. Multicomponent copper alloy according to claim 1, characterized inthat it contains from 0.01 to 0.06% P, finely distributed Ni phosphidephases being formed in the matrix.
 7. Multicomponent copper alloyaccording to claim 6, characterized in that the average grain size ofthe finely distributed Ni phosphide phases is less than 100 nm. 8.Multicomponent copper alloy according to claim 1, characterized in thatit contains from 0.1 to 2.5% Mn and from 0.1 to 1.5% Si. 9.Multicomponent copper alloy according to claim 8, characterized in thatit contains from 0.1 to 1.6% Mn and from 0.1 to 0.7% Si. 10.Multicomponent copper alloy according to claim 1, characterized in thatit has undergone at least one heat treatment at from 300 to 500° C. 11.Multicomponent copper alloy according to claim 1, characterized in thatit has undergone at least one heat treatment at from 600 to 800° C. 12.Multicomponent copper alloy according to claim 1, characterized in thatit has undergone a combination of at least one solution anneal at from600 to 800° C. and at least one age hardening at from 300 to 500° C. 13.Use of the multicomponent copper alloy according to claim 1 forfriction-bearing elements or jack connectors.